The present invention relates to alkoxysilane- and allophanate-functionalized coating materials, to a process for the production thereof and to the use thereof.
Polyurethanes have been established for many decades as high-value components for paint, adhesive, sealant and plastics systems. It is possible here for additional alkoxysilane groups to play an important role, for example with regard to network density, chemicals resistance and scratch resistance, primarily through the formation of siloxane and polysiloxane structures.
Molecules not only having alkoxysilane groups but also comprising isocyanate groups offer the option of introducing the functionalities that result as reaction products, siloxanes and polyurethane groups, through one component. Such substances have long been in use, for example in the form of isocyanatoalkyltrialkoxysilanes.
Alkoxysilane-terminated polyurethanes produced from isocyanatoalkyltrialkoxysilanes and alcohols are also known and are used, for example, for producing highly crosslinked, hard coating materials (e.g. EP 2676982 A1). The alkoxysilane-containing coating materials described in EP 2676982 A1, however, are disadvantageous in having only short potlives.
Allophanate-containing binders are known. Alkoxysilane-functionalized allophanates are also known. It is appropriate here to distinguish between various types, which are set out below, but which correspond neither in structure nor in application to alkoxysilane-functionalized allophanates present in the alkoxysilane- and allophanate-functionalized binder according to the invention.
For instance, the allophanates III (1) described in WO 2008/043722 A1 are obtained by reacting NCO-terminated allophanate-containing polyurethanes I (1) with isocyanate-reactive alkoxysilanes II (1) (e.g. aminoalkyltrialkoxysilane). The allophanate groups here are therefore in the centre of the polyurethane chain and the alkoxysilane function is attached via the terminal isocyanate group in the context of a urea function (structure III (1), equation 1).

DE 102005041953 A1 describes the reaction of a polyol I (2) having an average molecular weight of 3000-20 000 g/mol with an excess of isocyanatopropyltrimethoxysilane II (2) so that after polyurethane formation III (2) an allophanate IV (2) having two alkoxysilane functions per allophanate unit is formed.

In DE 102005041954 A1, a polyurethane I (3) is admixed with isocyanatopropyltrimethoxysilane II (3) and the mixture is heated until allophanate structures are formed. In this case, the alkoxysilane group is added onto the terminal nitrogen of the allophanate group III (3) (equation 3).

J. Kozakiewicz et al. published, in Progress in Organic Coatings 72 (2011) 120-130, the reaction of isocyanatopropyltrimethoxysilane I (4) with methanol to form the corresponding urethane II (4) and subsequently with hexamethylene diisocyanate trimer III (4). In the highly viscous allophanate IV (4) resulting therefrom, the alkoxysilane function is attached to the tertiary, central amine of the allophanate group (equation 4).

In the described application, the allophanate function serves as blocking agent for the hexamethylene diisocyanate trimer used as a crosslinker for hydroxy-functionalized polyester polyols.
Even today there is a need for new silane-containing coating materials having specific properties.